Bitcoin is a virtual and unregulated digital currency, not issued by any central bank. It has no central authority and it can be exchanged like currency notes. It maintains anonymity. It's price is $7749.39 as of July 31st 2018. Know more about bitcoins here
IMO Messenger app is one of the prominent video calling apps which enables you to chat with people miles away. It would be the better option without any odds like overcharge and loss of signals. The best thing is - It works well in the weak signals and it’s free. More about it here
Bugs in a website or a software leads to vulnerabilities and exploits. Many websites and software developers offer a deal called Bug Bounty Programs, also called vulnerability reward programs (VRPs) where individuals (Software Security Researchers and White hat hackers) get recognition and compensation for reporting these type of bugs.